In wire cut electric discharge machines, either the wire electrode or the workpiece is moved relative to the other within a horizontal plane ("the X-Y plane") determined by two perpendicular axes as the wire electrode travels between a pair of wire guides perpendicular to the X-Y plane. In many cases, the work piece is affixed to a work stand, and the work stand is attached to a table mounted on a bed movable within the X-Y plane.
Also known, as illustrated in FIG. 5, are wire cut electric discharge machines in which the table does not move, and each of the arms to which the wire guides are attached is supported by a part capable of moving within the X-Y plane. The wire cut electric discharge machine comprises a bed 1, a non-moving table 2 mounted on top of the bed 1, and a movable column 21. A work stand 7 is affixed to the table 2, and a workpiece W is attached to the work stand 7. A machining tank sidewall 8 which surrounds the workpiece W is also affixed the table 2.
A column 21 is mounted on the bed 1 so as to be movable in the X direction, and a ram 22 is mounted on top of the column 21 so as to be movable along the Y axis, which is perpendicular to the X axis. A head 9 is provided on the portion of ram 22 which protrudes toward the machining tank side, such that it can move in the Z axis which is perpendicular to the X-Y plane.
A wire supply device comprising a device to impart tension to a wire electrode E and multiple pulleys is provided on the machining head 9. A taper cut unit 23, formed of sliders 231 and 232, is provided on the bottom edge of the machining head 9. The slider 231 is movable in the U axis direction which is parallel to the X axis, and the slider 232 is movable in the V axis direction which is parallel to the Y axis. An automatic wire threader 13--the "AWT"--which automatically pushes the wire electrode E through a hole in the workpiece W, is attached to the taper cut unit 23. In the illustrated example, upper arm 11 is also attached on one edge to the taper cut unit 23, and an upper wire guide device 14 is attached to the other end of the upper arm 11. An approximately L-shaped lower arm 15 is affixed at one end to the bottom of the ram 22, and extends downward in the column 21 through a hole in the ceiling of the column 21. The lower arm 15 next penetrates the sidewall 8 of the horizontally extending machining tank, and a lower wire guide device 16 is attached to the other end of the lower arm 15.
During machining, the wire electrode E normally moves in the X-Y plane relative to the workpiece W, and travels between the pair of wire guide devices 14 and 16 perpendicular to the X-Y plane. For example, when fabricating a die with a tapered surface, machining is usually done by tilting the wire electrode E which travels between the pair of wire guide devices 14 and 16 by some angle away from the Z axis. With "taper cuts" of this type, the upper wire guide device 14 moves in the U-V plane which is determined by the orthogonal U and V axes, by means of the taper cut unit 23. The size of the taper cut unit 23 is limited by the machine's rigidity, such that the maximum movement of the upper wire guide device 14 is normally about 70 mm in both the U and V axes.
In recent years there has been a need for wire cut electric discharge machines having a large degree of movement in the U and V axes in order to form a sloped surface with a substantial angle on a workpiece of some thickness. A wire cut electric discharge machine with such features but without a loss of machine rigidity is illustrated in FIG. 6. The same reference numerals (as used in FIG. 5) are used to designate the same elements as in the wire cut electric discharge machine of FIG. 6, so an explanation thereof is omitted. A mechanical cover 100, which blocks electromagnetic radiation above a certain frequency in accordance with the law, covers the wire cut machine.
The mechanical cover 100, which blocks electromagnetic radiation above a certain frequency is accordance with EMC (electromagnetic compatibility) regulations, covers the wire cut electric discharge machine. A moving body 3 is mounted on a bed 1 so as to be movable along the X axis, and a moving body 4 is mounted on a column 21 so as to be moveable along the Y axis which is perpendicular to the X axis. The lower arm 15 is supported at one end by a moving body 4. A moving body 5 is mounted on the moving body 4 so as to be movable along the U axis which is parallel to the X axis, and a moving body 6 is mounted on the moving body 5 so as to be movable along the V axis which is parallel to the Y axis. A panel 10 is provided on the portion of the moving body 6 which protrudes toward the machining tank side, so as to be movable along the Z axis which is perpendicular to the X-Y plane. A wire supply device comprising a wire bobbin 12 around which is wound the wire electrode E, a device for imparting tension the wire electrode E, and multiple pulleys, is provided on the panel 10. Furthermore, the automatic wire threader 13 and the upper arm 11 are attached to the panel 10. A numerical control device 30 comprising a computer controls movement in the X axis, the Y axis, the U axis, the V axis, and the Z axis directions.
As is clear from the diagrams, the wire cut electric discharge machine in FIG. 6 provides a maximum movement for the moving body 5 and the moving body 6 which is greater than that of sliders 231 and 232 in FIG. 5. In recent wire cut electric discharge machines, a greater maximum movement is sought with respect to the U and V axes, as is a smaller installation footprint. Therefore when the panel 10 and the machining tank side wall 8 are designed for minimum size, there is a danger that these parts may be physically struck by other mechanical components. It is necessary, for example, to prevent the head 9 from striking other mechanical components such as the machining tank side wall 8 or the mechanical cover 100, or excessive overhang of the head 9.